How does Entity Graph differ from JOIN FETCH?

Entity Graph and JOIN FETCH are both used in JPA/Hibernate to optimize the loading of related entities, but they have different approaches and capabilities.

• JOIN FETCH is a directive in JPQL or Criteria API that indicates performing an SQL JOIN and immediately loading related entities. It is a strict method applied to a specific query and affects the SQL structure.

• Entity Graph is a declarative mechanism that allows describing which associations to load without changing the query. Entity Graph can be applied to different queries, making it more flexible and reusable.

Key differences:

• Entity Graph can be used for dynamic management of loading (fetch plan) without modifying JPQL.
• JOIN FETCH is embedded directly into the query and can lead to data duplication when multiple associations are involved.
• Entity Graph supports both eager (EAGER) and lazy (LAZY) loading, whereas JOIN FETCH is always eager.

Example of using Entity Graph:

@EntityGraph(attributePaths = {"orders", "profile"})
List<User> findAll();

JOIN FETCH example:

SELECT u FROM User u JOIN FETCH u.orders

In summary, Entity Graph is a more flexible and declarative way to manage loading, while JOIN FETCH is more explicit and query-specific.